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1. Supernova rates and luminosity functions from ASAS-SN I: 2014–2017 Type Ia SNe and their subtypes

   https://doi.org/10.1093/mnras/stae606  

   Desai, D D; Kochanek, C S; Shappee, B J; Jayasinghe, T; Stanek, K Z; Holoien, T_W -S; Thompson, T A; Ashall, C; Beacom, J F; Do, A; et al (May 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present the volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the V-band All-Sky Automated Survey for Supernovae (ASAS-SN) catalogues spanning discovery dates from UTC 2014 January 26 to UTC 2017 December 29. Our standard sample consists of 404 SNe Ia with $$m_{\mathrm{{\it V},peak}} \lt 17\, \mathrm{mag}$$ and Galactic latitude |b| > 15°. Our results are both statistically more precise and systematically more robust than previous studies due to the large sample size and high spectroscopic completeness. We make completeness corrections based on both the apparent and absolute magnitudes by simulating the detection of SNe Ia in ASAS-SN light curves. We find a total volumetric rate for all subtypes of $$R_{\mathrm{tot}} = 2.28^{+0.20}_{-0.20} \times 10^{4}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$ for $$M_{\mathrm{{\it V},peak}} \lt -16.5\, \mathrm{mag}$$ ($$R_{\mathrm{tot}} = 1.91^{+0.12}_{-0.12} \times 10^{4}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$ for $$M_{\mathrm{{\it V},peak}} \lt -17.5\, \mathrm{mag}$$) at the median redshift of our sample, zmed = 0.024. This is in agreement (1σ) with the local volumetric rates found by previous studies. We also compile LFs for the entire sample as well as for subtypes of SNe Ia for the first time. The major subtypes with more than one SN include Ia-91bg, Ia-91T, Ia-CSM, and Ia-03fg with total rates of $$R_{\mathrm{Ia-91bg}} = 1.4^{+0.5}_{-0.5} \times 10^{3}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, $$R_{\mathrm{Ia-91T}} = 8.5^{+1.6}_{-1.7} \times 10^{2}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, $$R_{\mathrm{Ia-CSM}} = 10^{+7}_{-7}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, and $$R_{\mathrm{Ia-03fg}} = 30^{+20}_{-20}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, respectively. We estimate a mean host extinction of $$E(V-r) \approx 0.2\, \mathrm{mag}$$ based on the shift between our V band and the Zwicky Transient Facility r-band LFs. 

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2. Carnegie Supernova Project: The First Homogeneous Sample of Super-Chandrasekhar-mass/2003fg-like Type Ia Supernovae

   https://doi.org/10.3847/1538-4357/ac19ac  

   Ashall, C.; Lu, J.; Hsiao, E. Y.; Hoeflich, P.; Phillips, M. M.; Galbany, L.; Burns, C. R.; Contreras, C.; Krisciunas, K.; Morrell, N.; et al (November 2021, The Astrophysical Journal)

   Abstract We present a multiwavelength photometric and spectroscopic analysis of 13 super-Chandrasekhar-mass/2003fg-like Type Ia supernovae (SNe Ia). Nine of these objects were observed by the Carnegie Supernova Project. The 2003fg-like SNe have slowly declining light curves (Δ m 15 ( B ) < 1.3 mag), and peak absolute B -band magnitudes of −19 < M B < −21 mag. Many of the 2003fg-like SNe are located in the same part of the luminosity–width relation as normal SNe Ia. In the optical B and V bands, the 2003fg-like SNe look like normal SNe Ia, but at redder wavelengths they diverge. Unlike other luminous SNe Ia, the 2003fg-like SNe generally have only one i -band maximum, which peaks after the epoch of the B -band maximum, while their near-IR (NIR) light-curve rise times can be ≳40 days longer than those of normal SNe Ia. They are also at least 1 mag brighter in the NIR bands than normal SNe Ia, peaking above M H = −19 mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark-energy experiments. Spectroscopically, the 2003fg-like SNe exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000–12,000 km s −1 ) in Si ii λ 6355 velocities at maximum light with no rapid early velocity decline, and no clear H -band break at +10 days. We find that SNe with a larger pseudo-equivalent width of C ii at maximum light have lower Si ii λ 6355 velocities and more slowly declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like SNe. The explosion of a C–O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core-degenerate scenario. 

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3. SN 2017fzw: A Fast-Expanding Type Ia Supernova with Transitional Features

   https://doi.org/10.3390/universe9060295  

   Huang, Jiayu; Li, Yangyang; Zeng, Xiangyun; Zheng, Sheng; Bird, Sarah A.; Zhang, Jujia; Esamdin, Ali; Iskandar, Abdusamatjan; Bostroem, K. Azaleee; Zeng, Shuguang; et al (June 2023, Universe)

   In this study, we analyzed the optical observations of a subluminous Type Ia supernova (SN Ia) 2017fzw, which exhibited high photospheric velocity (HV) at B-band maximum light. The absolute B-band peak magnitude was determined to be MmaxB=−18.65±0.13 mag, similar to 91bg-like SNe Ia. An estimation of the rate of decline for the B-band light curve was determined to be Δm15(B)=1.60±0.06 mag. The spectra of SN 2017fzw were similar to those of 91bg-like SNe Ia, with prominent Ti ii and Si ii λ5972 features at early phases, gradually transitioning to spectra resembling normal (mainly HV subclass) SNe Ia at later phases, with a stronger Ca ii NIR feature. Notably, throughout all phases of observation, SN 2017fzw displayed spectral evolution characteristics that were comparable to those of HV SNe Ia, and at peak brightness, the Si ii λ6355 velocity was determined to be 13,800 ± 415 km s−1 and a more pronounced Ca ii NIR feature was also detected. Based on these findings, we classify SN 2017fzw as a transitional object with properties of both normal and 91bg-like SNe Ia, providing support for the hypothesis of a continuous distribution of supernovae between these two groups. 

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4. Significant luminosity differences of two twin Type Ia supernovae

   https://doi.org/10.1093/mnras/stz3324  

   Foley, Ryan J; Hoffmann, Samantha L; Macri, Lucas M; Riess, Adam G; Brown, Peter J; Filippenko, Alexei V; Graham, Melissa L; Milne, Peter A (February 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The Type Ia supernovae (SNe Ia) 2011by, hosted in NGC 3972, and 2011fe, hosted in M101, are optical ‘twins,’ having almost identical optical light-curve shapes, colours, and near-maximum-brightness spectra. However, SN 2011fe had significantly more ultraviolet (UV; 1600 < λ < 2500 Å) flux than SN 2011by before and at peak luminosity. Several theoretical models predict that SNe Ia with higher progenitor metallicity should (1) have additional UV opacity and thus lower UV flux; (2) have an essentially unchanged optical spectral-energy distribution; (3) have a similar optical light-curve shape; and (4) because of the excess neutrons, produce more stable Fe-group elements at the expense of radioactive 56Ni and thus have a lower peak luminosity. Following these predictions, Foley and Kirshner suggested that the difference in UV flux between SNe 2011by and 2011fe was the result of their progenitors having significantly different metallicities. They also measured a large, but insignificant, difference between the peak absolute magnitudes of the SNe (ΔMV, peak = 0.60 ± 0.36 mag), with SN 2011fe being more luminous. We present a new Cepheid-based distance to NGC 3972, substantially improving the precision of the distance measurement for SN 2011by. With these new data, we determine that the SNe have significantly different peak luminosities (ΔMV, peak = 0.335 ± 0.069 mag). Consequently, SN 2011fe produced 38 per cent more 56Ni than SN 2011by, consistent with predictions for progenitor metallicity differences for these SNe, although alternative models may also explain this difference. We discuss how progenitor metallicity differences can contribute to the intrinsic scatter for light-curve-shape-corrected SN luminosities, the use of ‘twin’ SNe for measuring distances, and implications for using SNe Ia for constraining cosmological parameters. 

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5. SN 2019nyk: A rapidly declining Type II supernova with early interaction signatures

   https://doi.org/10.1051/0004-6361/202348642  

   Dastidar, Raya; Pignata, Giuliano; Dukiya, Naveen; Misra, Kuntal; Hiramatsu, Daichi; Silva-Farfán, Javier; Andrew_Howell, D; Azalee_Bostroem, K; Singh, Mridweeka; Gangopadhyay, Anjasha; et al (May 2024, Astronomy & Astrophysics)

   We present an optical photometric and spectroscopic analysis of the fast-declining hydrogen-rich Type II supernova (SN) 2019nyk. The light curve properties of SN 2019nyk align well with those of other fast-declining Type II SNe, such as SNe 2013by and 2014G. SN 2019nyk exhibits a peak absolute magnitude of −18.09 ± 0.17 mag in theVband, followed by a rapid decline at 2.84  ±  0.03 mag (100 d)⁻¹during the recombination phase. The early spectra of SN 2019nyk exhibit high-ionisation emission features as well as narrow H Balmer lines, persisting until 4.1 d since explosion, indicating the presence of circumstellar material (CSM) in close proximity. A comparison of these features with other Type II SNe displaying an early interaction reveals similarities between these features and those observed in SNe 2014G and 2023ixf. We also compared the early spectra to literature models, estimating a mass-loss rate of the order of 10⁻³M_⊙yr⁻¹. Radiation hydrodynamical modelling of the light curve also suggests the mass loss from the progenitor within a short period prior to explosion, totalling 0.16M_⊙of material within 2900R_⊙of the progenitor. Furthermore, light curve modelling infers a zero-age main sequence mass of 15M_⊙for the progenitor, a progenitor radius of 1031R_⊙, and an explosion energy of 1.1 × 10⁵¹erg. 

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